[dmd-concurrency] draft 5

[Kevin Bealer]

On Wed, Jan 20, 2010 at 1:39 AM, Sean Kelly <sean at invisibleduck.org> wrote:

> void fnB() {
>    // do something that takes a while
> }
> void fnA() {
>
auto tid =

>    spawn( &fnB );
>
tid.wait();

> }
>
> void main() {
>    auto tid = spawn( &fnA );
>    tid.wait();
> }
>
> The main thread doesn't know the thread running fnB exists so it can't wait
> for it, even if it's doing completely legitimate work and shouldn't be
> interrupted.  How can I trivially rewrite this program so it completes
> without error?
>
> On Jan 19, 2010, at 10:28 PM, Andrei Alexandrescu wrote:
>
> > That would certainly work, but honest to God I am completely infatuated
> with the proposed model. It's simple, no need for a new "daemon" concept,
> and avoids very easily and elegantly the unpleasant zombie situation when
> main has finished but is somewhere in limbo mode hoping for some other
> thread to end.
> >
> > Also, look at how simple it makes all examples. It's a dream come true.
> I've been thinking of a correct shutdown protocol for years, and this is
> better than anything I've ever tried.
> >
> > I'd be ok with doing what Java does if we find an Achilles' heel of the
> current model. If not, I suggest we go with it and let users handle their
> own daemons (heh) in main().
> >
> >
> > Andrei
> >
> > Sean Kelly wrote:
> >> On Jan 19, 2010, at 9:49 PM, Andrei Alexandrescu wrote:
> >>> Sorry, I was unclear on that. Once the application is shutting down,
> any call to concurrency-related function, pending or new, will result in the
> Shutdown exception.
> >> Why couldn't any threads that cared simply watch() the main thread so
> they'll be notified when it terminates?  Forcing this behavior on the user
> means that if an app wants to do anything in a separate thread that doesn't
> communicate with the main thread, he'd have to make sure the main thread
> joined every other thread in the process to keep from interrupting it.
> >> Druntime follows the Java model of having an isDaemon field on the
> Thread object.  If isDaemon is false for a thread T1 then the main thread
> will silently wait for T1 to terminate before shutting down the app.  If
> isDaemon is true however, T1 will be terminated forcibly by the OS as the
> process exits.  Perhaps we could provide this ShutdownException behavior
> only to daemon threads as a replacement for the messy shutdown they have
> now?
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